EFFECT OF ETHANOL, PROPYLENE-GLYCOL AND GLYCEROL ON THE INTERACTION OF METHYL AND PROPYL P-HYDROXYBENZOATE WITH STAPHYLOCOCCUS-AUREUS AND PSEUDOMONAS-AERUGINOSA

Go-solvents ethanol, propylene glycol and glycerol were used to increa se the aqueous concentrations of methyl and propyl p-hydroxybenzoate a bove their saturation solubility. The increased aqueous concentration of parabens in co-solvent solutions was associated with increased anti bacterial activity against Staphylococcus aureus and Pseudomonas aerug inosa, but the extent of this effect increased with increasing hydroph obicity of the co-solvent. Addition of co-solvents to aqueous solution s of parabens caused a reduction in their octanol/water partitioning a nd a reduction in the uptake of the parabens by the cells, the extent of the reduction increasing as the hydrophobicity of the co-solvent in creased. The addition of co-solvents also potentiated cell membrane da mage as evidenced by leakage of radio-labelled phosphate from parabens -treated cells, but in this situation the extent of the damage was cor related with increasing hydrophobicity of the co-solvent. The results indicate that the increase in antibacterial activity of parabens prese rvatives in co-solvent solutions can largely be accounted for by their combined effects on the integrity of the cell membrane. (C) 1997 Else vier Science B.V.